The present invention relates to pneumatic tires, and more particularly, to a pneumatic tire which can improve uneven wear resistance and wet performance.
In general, pneumatic tires including a tread surface having a rib pattern, used for heavy duty vehicles such as buses and trucks, receive greater traverse shear strain at the end portions of the ribs than at the center portion thereof when the tires are engaged with a ground. Therefore, the compression amount of the end portions of the ribs in the circumferential direction and widthwise direction of the tire increases, whereby the end portions of the ribs locally go up in ground contact pressure, resulting in that such uneven wear that the end portions of the ribs wear more rapidly is apt to occur. In particular, pneumatic tires having rib patterns, used for the steering-wheel tires of trucks and buses which mainly travel a long distance consecutively at a high speed, strongly have such tendencies.
It has been conventionally known, for example, to provide sipes in the end portions of the ribs facing the circumferential grooves as measures for the above (see Japanese Patent Application Kokai Publication Nos. 2002-36819 and 2005-59620, for example). The sipes lower the ground contact pressure of the end portions of the ribs, whereby the ground contact pressure of the tread surface is more even, allowing uneven wear of the ribs to be reduced. There has also been proposed a technique of providing a rib with a row of sipes comprising tire-circumferentially extending sipes disposed at prescribed intervals in the circumferential direction of the tire (see Japanese Patent Application Kokai Publication No. 2000-16024, for example).
However, demands for tire performance improvements from the market have never stopped, and further improvement in uneven wear for pneumatic tires having rib patterns is required. The pneumatic tires having rib patterns have disadvantages that they are inferior in wet performance to pneumatic tires having block patterns; improvement of the wet performance is also required.